This invention relates particularly to the so-called "smooth top" cookers of the type in which a smooth top normally of glass ceramic overlays one or more generally circular electric heater elements supported on a layer of thermal and electrical insulating material such that the element is spaced from the top. In use, a utensil placed on the top over an element is heated by the transmission of heat from an element to and through the top by air convection and infra red radiation. Such elements are referred to herein as "radiant heaters". The insulating material substantially prevents heat being transmitted away from the element except towards the top and as the preferred materials for the top are essentially thermally non-conductive, only areas of the top which are "exposed" to the element will be heated. In order to prevent heat being transmitted to parts of the top not covered by a utensil placed thereon, a peripheral wall of insulating material is also normally provided around the coil.
While the arrangement described above has been very successful, its best use efficiency is limited to use with utensils having bases of area substantially equal to that of the heater or "exposed" area of the top. Where the areas are not equal, either the heating of the utensil is non-uniform, or local areas of the top are exposed which is wasteful of heat.